Of course, there's still a chance the deal will not go through. The Saudi government is still reportedly in early-stage talks, and has not made any final decisions on the deal. Not to mention the fact that oil is hovering around its lowest prices in decades.

But JPMorgan and Klein have secured prized roles on the deal of a lifetime nonetheless.

Klein, who started his firm as a one-man band in 2012, landed a major role on the $130 billion Dow-DuPont deal announced in December.

He spent more than two decades at Citigroup, rising to the role of CEO of global banking and then moving to Europe to take responsibility for a build-out of the bank's investment-banking business in the region. He left Citigroup in 2008, and was paid north of $25 million to not compete with the firm.